The long term goal of these experiments is to define the correlation between functional properties in primary auditory cortex (AI) and the patchy thalamocortical projections that arise from the ventral division of the medial geniculate body (MGV). Unlike other sensory systems, the thalamocortical pathways that subserve functional maps AI are not well defined. A patchy or discontinuous organization of functional properties exists in AI of several species. There also exists a patchy or discontinuous thalamocortical projection pattern from the ventral division of the MGB to AI. Further, two major areas (pars lateralis and pars ovoidea) within the MGV that project to AI have been differentiated by cellular architecture, functional properties and immunocytochemistry, and there is evidence to suggest the existence of multiple parallel pathways from MGV to AI. These multiple pathways may encode different functional properties. In specific aim 1 we will determine the relationship between patchy TC projections arising from MGV to AI and functional response clusters in AI. In specific aim 2 we will characterize TC projections to AI arising from the LV and OV to determine if they project in a unique way to AI and give rise to novel classes of functional properties. BDA injections will target the IV and OV specifically. In specific aim 3 we will characterize and compare the TC projection patterns single, fully reconstructed relay cells in the MGV. The proposed studies will define the anatomical substrates for functional properties that exist in AI and characterize multiple parallel circuits from MGV to AI.